The present disclosure relates to a liquid supply unit for supplying liquid stored in a liquid storage container to a liquid injection head and a liquid injection device to which the liquid supply unit is applied.
For example, in an ink jet printer, a liquid injection head for injecting a tiny amount of ink (liquid) to a print object is used. Ink is supplied to this liquid injection head from an ink cartridge (liquid storage container) storing the ink through a predetermined supply passage. Conventionally, a liquid injection device is known in which a liquid supply unit (valve unit) including a pressure chamber for setting a discharge hole of a liquid injection head to a negative pressure is arranged in a supply passage in the case of supplying ink from an ink cartridge to the liquid injection head by a water head difference. By disposing the liquid supply unit for generating the negative pressure, unlimited dripping of the ink from the discharge hole is suppressed even if the ink is supplied by the water head difference.
A conventional liquid supply unit adopts such a structure that a part of a pressure chamber set to a negative pressure is defined by a flexible film and a pressing plate (pressure receiving plate) attached to this flexible film directly presses a movable valve. The movable valve is biased in a direction opposite to a direction of the pressing by a biasing member. If a negative pressure degree of the pressure chamber increases due to the suction of ink by the liquid injection head, the movable valve is pressed against the pressing plate to move according to a displacement of the flexible film, an ink supply passage into the pressure chamber is opened and the ink flows into the pressure chamber. If the negative pressure degree of the pressure chamber decreases due to this inflow of the ink, the movable valve is moved in a reverse direction by a biasing force of the biasing member and the pressure chamber returns to a sealed state.